Recovery of krypton and xenon



Aug. 18, 1936. J. SCHLITTV 2,051,576

RECOVERY OF KRYPTON AND XENON Filed April 6, 1956 INVENTOR se 64' z.Sch/1 19 ATTORNEYS Patented Aug. 18, 1936 RECOVERY OF KRYPTON AND XENONJoseph L. Schlitt, Darlen, Conm, assignor to Air Reduction Company,Incorporated, New York, N. Y., a. corporation of New York ApplicationApril 6, 1936, Serial No. 72,885

'7 Claims.

This invention relates to the separation of the rare gases krypton andxenon from the atmosphere .and the recovery of these gases in quantitlessuch as to permit commercial applications thereof.

Air contains only minute proportions of krypton and xenon, and theordinary methods of separating air for the recovery of nitrogen, oxygenand argon take no account of the rarer gases. No practicable commercialmethod of recovering these gases has been available heretofore.

It is the object of the present invention to provide a simple, practicaland effective method of separating and recovering krypton and xenon fromthe atmosphere.

A further object of the invention is the provision of a method oftreating relatively large volumes of air at low cost to permit therecovery of krypton and xenon therefrom. These gases are thus madeavailable for various commercial and industrial uses.

In carrying out the present invention, no attempt is made to recover allof the nitrogen, oxygen and argon as separate gases of substantialpurity, since the primary function of the method is the recovery of therarer gases krypton and xenon. The constituents of the atmosphere aresubjected to primary separation to afiord a liquid fraction which isutilized for the purpose of concentrating krypton and xenon fromadditional quantities of air. The subsequent rectification of the liquidenriched in krypton and xenon with other liquids and vapors producedaffords a liquid further enriched in krypton and xenon. This liquid issubjected then to a further rectification to effect separation ofoxygen, leaving a liquid concentrate rich in krypton and xenon which canbe withdrawn'and utilized. A

portion of the oxygen and also of the nitrogen is also recoverable, butthe major portion of all of the air treated is returned to theatmosphere as a gaseous mixture from which only the krypton and xenonhave been removed.

to be treated, after initial compression to a suitable pressure andcooling in the usual exchangers (not shown) is introduced through a pipe5 to the bottom compartment 6 of a column I. The air passes upwardlythrough tubes 8 immersed in a liquid product accumulated as hereinafterdescribed, and thence downwardly through tubes 9 into a collector III.In passing through the tubes 8, the air is subjected to selectiveliquefaction with the resulting formation 1 of a. liquid more or lessclosely in phase equilibrium with the composition of the air, that is tosay, a liquid containing approximately from 21 to 45% of oxygen, thebalance being nitrogen with some of the argon and a considerable portionof the krypton and xenon of the air treated. The liquid flows backwardlyand accumulates in the compartment 6. The unliquefied residue,consisting largely of nitrogen, in passing downwardly through the tubes9 is also liquefied and accumulates in the collector Ill. This liquidalso may contain some krypton and xenon as well as a portion of theargon.

In the usual method of treating air to separate oxygen and nitrogen,these two liquids are immediately delivered at different levels to arectifier l to effect a separation of the constituents. In the methodforming the subject matter of the present application, however, one orthe other of these liquids, for example, the one condensed in tubes 8and collected in compartment 6 instead of being immediately delivered torectifier l, is conducted while still under pressure to coil 48surrounded by liquid enriched in oxygen as well as krypton and xenonlocated in the base of a column l3. The liquid in the coil 48 issubcooled by evaporating a portion of the liquid surrounding the coiland is then delivered by means of valve 49 and pipe 50 to a rectifierI3. provided with the usual trays IS. The liquid in fiowing downwardlyover trays l6 comes into contact with a relatively large volume of airunder. low pressure introduced into the middle of rectifier I3 by meansof pipe H. The efiect will be to wash from the large volume of enteringair, by means of the liquid introduced through the pipe 50,substantially all of the krypton and xenon together with some of theoxygen while the eflluent leaving rectifier l3 through pipe 23 willconsist of a gaseous mixture, principally nitrogen but containing oxygenand argon. The efiluent may be sent to an exchanger through a valve 24and pipe 25.

The liquid, enriched in krypton and xenon, which accumulates in thebottom of the rectifier I 3 is withdrawn through pipe 21, controlled byvalve 30 and is delivered to an intermediate level of the column I inwhich the usual rectification trays 29 are disposed. The liquid and anyresidual vapor from the collector I0 is delivered through a pipe l2,valve 3| and pipe 28 to the top of the rectifier I and flows downwardlyover the trays '29 therein to efi'ect a further washing of the vaporsarising from the lower portion of the rectifier. If the liquid from thecollector I 0 is delivered to the coil 48, the liquid from the ment.

compartment 6 will be delivered to the top of the rectifier I. Aspreviously indicated, either of the liquids accumulating in thecompartment 6 and collector Hi can be used as a wash liquid for thelarge volume of air in the rectifier l3.

In flowing downwardly over the trays 29, the two liquids introduced tothe column I are subjected to rectification with vapors arising from thebody of liquid surrounding tubes 3 and 9. This liquid is vaporized inthe initial condensation of the entering air, and the resulting ,vapors,together with those formed during the rectification, pass upwardlythrough the column I and escape as an eiliuent consisting principally ofnitrogen with some or all of the argon present in the liquid, through apipe 33. The liquid flowing downwardly through the column finallyaccumulates about the tubes 8 and 9 and consists principally of oxygenand substantially all of the krypton and xenon which has been separatedfrom the air entering through the pipes 5 and H,

A portion of the liquid, together with vapors from the lower part of thecolumn I, is delivered through pipes 34 and 35 controlled by valves 36and 31 to intermediate levels of an auxiliary rectifier 38 containingthe usual trays 39 and having at the bottom a coil 40 which is suppliedwith air, previously compressed and cooled, through a pipe 4!. Intraveling through the coil, the air causes vaporization of the liquidsurrounding the coil and is itself liquefied, and, it may be, somewhatsubcooled. The liquid travels through the pipe 42 and valve 32 to thecompartment 6, thus joining the liquid accumulating in that compart- Thevapor passes upwardly through the trays in contact with the downwardlyflowing liquid and passes finally through tubes 43 of a condenser whichis cooled by the eiliuent escaping from the column I through the pipe33. A valve 44 controls the flow of the effluent which escapes finallythrough a pipe 45 to an exchanger. By utilizing the pipe 26 a portion ofthe efliuent from the rectifier I3 may be similarly utilized. Thecondenser 43 separates from the vapors a liquid which becomes muchconcentrated in krypton and xenon when it reaches the bottom ofrectifier 38. The eilluent from this rectifier escapes through a pipe 46controlled by a valve 48 and consists of substantially pure oxygen whichmay be delivered through an exchanger to a suitable collector in whichthe oxygen may be accumulated for use. The liquid at the bottom of therectifier may be withdrawn through a pipe 41 controlled by a valve 49.It consists of a concentrate of krypton and xenon and is the principalproduct of the method as described. It may be utilized after furtherpurification for any desired purpose.

From the foregoing description it is very evident that the methodforming the subject matter of this application is an eflicient andpracticable method of extracting the krypton and xenon from largequantities of atmospheric 'air while at the same time an air separationapparatus for the production of high purity oxygen is operated inconnection therewith. The relation between the separation of the severalconstituents of air and the procedure by which krypton and xenon areextracted from a large quantity of air not I otherwise treated is suchthat an important advantage and economy in the air separation meth-. oditself is secured. This arises from the fact that one of the two liquidsinto which the air entering the rectifier I is converted is enriched in10 oxygen by reason of its passage through the krypton-xenon rectifierl3. That is to say, the liquid entering the krypton-xenon rectifierthrough pipe 50 and re-entering the rectifier I through pipe 21 carriesa substantially higher 15 percentage of oxygen after leaving thekryptonxenon rectifier than when it enters. This is due in part to thelower pressure prevailing in rectifier l3 compared to that in the tubes3 and in part due to the coil 43 located at the base of rec- 20 tifierl3. The method, as will be evident, affords the possibility of treatinglarge quantities of air and the recovery therefrom in a simple andsatisfactory manner of the krypton and xenon content of the air,together with a separate portion 25 consisting of oxygen in substantialpurity. Thus, krypton and xenon in quantities enabling the use of theseproducts for various commercial purposes are made available.

Various changes may be made in the details of 30 the procedure andapparatus employed without departing from the invention or sacrificingany of the advantages thereof.

I claim:

1. The method of recovering krypton and xenon from the atmosphere whichcomprises subjecting compressed and cooled air to selective liquefactionto separate two liquid fractions, utilizing one of the fractions to washkrypton and xenon from a relatively large volume of gaseous air andrectifying the resulting liquid rich in krypton and xenon with the otherliquid fraction produced by selective liquefaction and vapors resultingfrom partial evaporation of the liquid product.

2. The method of recovering krypton and xenon from the atmosphere whichcomprises subjecting compressed and cooled air to selective liquefactionto separate two liquid fractions, utilizing one of the fractions to washkrypton and xenon from a relatively large volume of gaseous air,rectifying the resulting liquid rich in krypton and xenon with the otherliquid fraction produced by selective liquefaction and vapors resultingfrom partial evaporation of the liquid product, and subjecting theliquid product to an auxiliary rectification to produce a liquidconcentrate containing the major portion of the krypton and xenon in theair treated and an eilluent consisting of oxygen exceeding in quantitythe amount thereof in the air subjected to initial selectiveliquefaction.

3. The method of recovering krypton and xenon from the atmosphere whichcomprises subjecting compressed and cooled air to selective liquefactionto separate two liquid fractions, subcooling and utilizing one of thefractions to wash krypton and xenon from a relatively large volume ofgaseous air and rectifying the resulting liquid rich in krypton andxenon with the other liquid fraction produced by selective liquefactionand vapors resulting from partial evaporation of the liquid product.

4. The method of recovering krypton and xenon from the atmosphere whichcomprises subjecting compressed and cooled air to selective liquefactionto separate two liquid fractions, subcooling and utilizing one of thefractions to wash krypton and xenon from a relatively large volume ofgaseous air, rectifying the resulting liquid rich in krypton and xenonwith the other liquid fraction produced by selective liquefaction andvapors resulting from partial evaporation of the liquid product, andsubjecting the liquid product to an auxiliary rectification to produce aliquid air, rectifying the resulting liquid rich in krypton and xenonwith the other liquid fraction produced by selective liquefaction andvapors resulting from partial evaporation of the liquid product,

' subjecting the liquid product to an auxiliary rectification to producea liquid concentrate containing the major portion of the krypton andxenon in the air treated and an efliuent consisting of oxygen exceedingin quantity the amount thereof in the air subjected to initial selectiveliquefaction, and condensing a portion .of the effluent from theauxiliary rectification to wash krypton and xenon from the vaporsproduced therein.

6. The method of recovering krypton and xenon from the atmosphere whichcomprises subjecting compressed and cooled air to selective 5liquefaction to separate two liquid fractions, subcooling and utilizingone of the fractions to wash krypton and xenon from a relatively largevolume of gaseous air, rectifying the resulting liquid rich in kryptonand xenon with the other liquid fraction produced by selectiveliquefaction and vapors resulting from partial evaporation of the liquidproduct, subjecting the liquid product to an auxiliary rectification toproduce a liquid concentrate containing the major portion of the kryptonand xenon in the air treated and an effluent consisting of oxygenexceeding in quantity the amount thereof in the air subjected to initialselective liquefaction, and condensing a portion of the efliuent fromthe auxiliary rectification to 0 wash krypton and xenon from the vaporsproduced therein.

7. The method of recovering krypton and xenon from the atmosphere whichcomprises initially separating the air by cooling and liquefaction intoat least two separate liquid fractions, utilizing one of the fractionsto wash krypton and xenon from a relatively large volume of gaseous airand rectifying the resulting liquid rich in krypton and xenon with otherliquids and vapors produced inthe initial separation and subsequentrectification.

JOSEPH L. SCHLI'IT.

